1. Field of the Invention
This invention relates to methods and apparatus for analyzing the properties of microscopic specimens by detecting the radiation emanating from elemental points on an area of the object at a plurality of different wavelengths and performing statistical, multi-variate analysis on the detected sets of points to identify each with one or more of a plurality of spectral signatures.
2. Prior Art
A variety of sophisticated techniques exist for analyzing properties of microscopic specimens in general, and particularly biological specimens by measuring the radiation from the specimens at a plurality of different wavelengths. For example, experimental work has been conducted in forming a series of photograhs of microscopic specimens employing different filters with each photograph to obtain images of the object at a series of particular wavelengths of interest. These images were then combined in some manner to obtain composite mappings showing spectral differences in a single image. Another related technique employed a spectrophotometer or spectroradiometer to obtain spectra from a number of spatially separated points on an object. Microspectrophotometers are used in this manner to obtain quantitative information about cytological or hystological specimens.
The "film-filter" techniques generate useful maps which segregate the various areas of an object's surface as a function of their spectral properties. Similarly, microspectroscopic techniques may be employed to obtain information relating to the properties of a plurality of points on an object and a mapping may be prepared on that basis. However, with these techniques the problem of identifying the nature of each point based on the spectral information from the point is extremely difficult and time consuming.
Independently of consideration of these problems, over the past few years extremely powerful techniques have been developed for extracting meaningful information regarding the earth's surface by overflying the surface with aircraft or spacecraft and detecting the spectral radiance of the underlying points in a number of properly chosen spectral bands. The power of this technique lies in its ability to identify the radiation spectrum of each point with known physical materials based not only on the information from each point by itself, but also on a statistical comparison of the radiation set from each point with a plurality of previously developed spectral signatures of known classes of materials, employing statistical multi-variate analysis. When the radiation from each elemental point in a scene is sensed in a relatively large number of spectral bands, i.e., 5-25, as is often required to differentiate between similar numbers of possible materials on a statistically meaningful basis, a relatively large number of calculations are required to perform the analysis (typically about 1,000 calculations per scene point) and until recently the magnitude of these calculations presented a substantial obstacle to the use of such procedures. However, special purpose computers have now been developed to perform these calculations at rates in the range of 10.sup.5 points per second. As a result, it has now become practical to process an image data set from an aircraft or spacecraft at rates of about 10.sup.7 picture elements per minute. This has made it possible to analyze geographical features, crops, and the like, in a truly meaningful manner.